The present invention relates to nuclear magnetic resonance relaxometry methods for quantifying bitumen and/or water in an ore sample including bitumen, water and solids.
Nuclear magnetic resonance (xe2x80x9cNMRxe2x80x9d) relaxometry logging tools are well known in the petroleum and natural gas exploration industry. However, their use has been limited to conventional light oil exploration such as in the Texas chalk formations or the North Sea sandstone formations because conventional low-field NMR does not yield meaningful results when applied to heavy oils and bitumen. The oil typically found in the oil sands deposits found in Northern and Eastern Alberta is heavy oil or bitumen.
The NMR signal obtained from heavy oil and bitumen formations or ore samples can consist of both a hydrocarbon signal and a water signal. Each NMR signal can further characterise both mobile and immobile fluids in porous media. However, as the viscosity of the hydrocarbon phase increases, and the NMR signal shifts towards shorter relaxation times, the composite NMR signal for the sample becomes very complicated. Because of its elevated viscosity, the relaxation characteristics of heavy oil and bitumen become largely undetectable by conventional low-field NMR tools. As a result, conventional methods of NMR detection fail to recognise precisely the hydrocarbon components.
It is useful to determine oil, water and solids content in a sample of bitumen bearing oil sands. Such determination is typically performed with a Dean Stark analysis which is a volumetric technique which relies upon physical separation of the individual components of a sample. However, the accuracy of Dean Stark analysis is sometimes questionable if the analysis is not done in a painstakingly careful manner. If done properly, with a view to accuracy, the analysis is a lengthy and complicated process, requiring specialized equipment.
Therefore, there is a need in the art for a system of determining the oil, water and/or solids content of heavy oil or bitumen bearing oil sands samples utilizing NMR and which provides relatively quick and accurate results.
The present invention is directed to methods using NMR technology for the quantitative determination of oil, water and solids as an alternative to conventional Dean Stark assays. The present invention is based on the discovery that while the amplitude of the water component of a NMR signal is only weakly temperature dependent, the oil component of the signal is very temperature dependent. At lower temperatures, the bitumen component is largely undetectable by a NMR relaxometer. At an elevated temperature, most of the bitumen component signal may be recovered. The inventors have developed methods by which the amplitude of the bitumen signal may be determined by comparing the low temperature combined signal with the high temperature combined signal. The signal amplitude may then be converted to a weight percentage value.
Therefore, in one embodiment of the invention, the invention is a method of determining the composition of a sample comprising heavy oil or bitumen and water, said method comprising the steps of:
(a) determining the NMR spectrum of the sample at a low temperature between about 0xc2x0 C. to about 50xc2x0 C.;
(b) determining the NMR spectrum of the sample at a high temperature between about 50xc2x0 C. to about 100xc2x0 C.;
(c) creating a differential spectrum where xcex94A=AHigh Txe2x88x92ALow T 
(d) determining the water content by summing the amplitudes of the low temperature spectrum for the T2 range where 2.5 ms less than T2 less than 3000 ms and dividing by the AI of water;
(e) determining the oil content by summing
i. the amplitudes of the high temperature spectrum in the T2 range where in the differential spectrum, xcex94A has a negative value; and
ii. the amplitudes of the differential spectrum where xcex94A has a positive value and dividing by the AI of oil at the high temperature.
Preferably, the low temperature is between about 20xc2x0 C. to about 40xc2x0 C. and more preferably it is about 30xc2x0 C. Preferably the high temperature is between about 70xc2x0 C. to about 90xc2x0 C. and more preferably it is about 80xc2x0 C.
The solids content of the sample may be determined by subtracting the oil and water content from the total weight of the sample.
In another aspect, the invention may comprise a system for determining the composition of a sample comprising bitumen or heavy oil and water in a porous media, said system comprising:
(a) means for determining the NMR T2 relaxation time spectrum of the sample at a low temperature between about 0xc2x0 C. to about 50xc2x0 C.;
(b) means for determining the NMR T2 relaxation time spectrum of the sample at a high temperature between about 50xc2x0 C. to about 100xc2x0 C.;
(c) means for creating a differential spectrum where xcex94A=AHighxe2x88x92ALow 
(d) means for determining the water content by summing the amplitudes of the low temperature spectrum for the T2 range where 2.5 ms less than T2 less than 3000 ms and dividing by the AI of water; and
(e) means for determining the heavy oil or bitumen content by summing
i. the amplitudes of the high temperature spectrum in the T2 range where, in the differential spectrum, xcex94A has a negative value; and
ii. the amplitudes of the differential spectrum where xcex94A has a positive value; and dividing by the AI of oil at the high temperature.